The present invention relates to the field of integrated circuits, and more particularly, to an integrated circuit including a threshold amplifier.
Integrated circuits are extensively used in a wide variety of environments. To meet all the needs of the market, it is sometimes necessary to plan for manufacturing options suited to specific goals. The management of these manufacturing options is costly because it implies different sets of manufacturing masks, different sets of tests, etc.
If we take the example of applications in highly noisy environments, for example automobile applications, it is especially necessary to filter the logic power supply applied to the integrated circuit. It is usual for this purpose to provide a Schmitt trigger circuit. This well-known circuit comprises an inverter stage associated with a hysteresis threshold-setting stage, by which two switching thresholds are obtained. The difference in voltage between these two thresholds gives the value of the hysteresis. Between these two thresholds, no switching of the inverter stage is possible. This characteristic is especially used to obtain a clean signal from a noisy signal.
However, Schmitt trigger type circuits have some drawbacks. They are slower to switch over than a simple inverter. Furthermore, there is always an active feedback loop so that the trigger is in a state of permanent power consumption, even in standby mode. Finally, it is hard to use them in low-voltage applications. For example, in CMOS technology, the switching thresholds defined for 0 and 1 are 0.3 Vcc and 0.7 Vcc, respectively. At low supply voltage, these 0.3 Vcc and 0.7 Vcc levels impose a respective operation of the N and P transistors at levels close to their threshold voltage. Thus, the Schmitt trigger circuit, which raises the threshold of the N and P input transistors by the substrate effect, is unfavorable to the detection of the 0.3 Vcc and 0.7 Vcc levels at low voltage.
This is why a manufacturing option is usually provided for these circuits. In a manufacturing option for noisy applications, the Schmitt trigger circuit is entirely implanted with the inverter stage and the hysteresis threshold-setting stage. For non-noisy applications or low-voltage applications, only the inverter stage, which does not have the above-mentioned drawbacks, is implanted. For example, an appropriate metal mask may be used to make the corresponding interconnections of the hysteresis threshold-setting stage.
An object of the invention is to provide an integrated circuit suited to different applications.
Another object of the invention is to reduce the manufacturing cost of such integrated circuits.
These and other objects, advantages and features of the invention are provided by a threshold amplifier that comprises a Schmitt trigger with hysteresis for high levels of the logic supply voltage and operates like a simple inverter for low levels of the logic supply voltage. Thus, there is an automatic switching from one type of operation to the other according to the level of the power supply voltage.
The invention relates to an amplifier of this kind and its use in an integrated circuit, especially to filter external logic signals. The invention therefore relates to a threshold amplifier receiving a logic supply voltage and a ground voltage as supply voltages and comprises a Schmitt trigger with an inverter stage and a stage for setting the high and low hysteresis thresholds, wherein the amplifier comprises a circuit for disabling the hysteresis stage as a function of the level of the logic supply voltage.
Other features and advantages of the invention are described in detail in the following description given by way of a non-restricted indication with reference to the appended figures, of which:
FIG. 1 shows a Schmitt trigger circuit using CMOS technology according to the prior art;
FIG. 2a shows the transfer curve of the circuit shown in FIG. 1;
FIG. 2b shows the shape of a signal recovered at the output of the circuit shown in FIG. 1 from a noisy input signal;
FIG. 3 shows a threshold amplifier according to the present invention;
FIG. 4 shows a variation of the value of the hysteresis with the supply voltage in a threshold amplifier according to the present invention;
FIGS. 5a and 5b show the influence on the hysteresis of the proportionality factor of the current mirrors in a threshold amplifier according to the present invention; and
FIG. 6 shows an integrated circuit comprising several threshold amplifiers according to the present invention for filtering input signals.